1. Technical Field
The present invention relates to an organic semiconductor compound having particularly good solvent solubility and semiconductor characteristics, an organic semiconductor thin film, an organic semiconductor coating liquid and an organic thin film transistor. In addition, the invention relates to novel methods for producing bis(benzo[4,5]thieno)[2,3-b:3′2′-e][1,4]dithiin and bis(benzo[4,5]thieno)[2,3-b: 2′3′-e][1,4]dithiin.
2. Related Art
Recently, as semiconductor materials for thin film transistors (TFTs), much attention has been focused on organic semiconductor materials. The organic semiconductor material facilitates the formation of a thin film by using a simple and easy technique such as spin coating or vacuum vapor deposition. As another advantage using the organic semiconductor material for TFTs, temperature during film forming process can be reduced compared to the formation of a well-known TFT made of amorphous or polycrystalline silicon. Low temperature process allows the formation of a thin film even on a low heat-resistant plastic substrate. Consequently, weight and cost reductions of a display can be realized, and moreover, for example, diversified application possibilities by taking advantage of flexibility of the plastic substrate will be expected.
Carrier mobility is among important physical parameters of the organic semiconductor material. Due to inherently weak intermolecular interaction force thereof, the organic semiconductor material strongly exhibits the properties of molecules themselves and in particular, the carrier mobility thereof is small compared to inorganic semiconductor materials. This weakness has been a significant impediment to practical application thereof.
The organic semiconductor material is roughly classified into two groups, low molecules and high molecules. The low molecular materials that have been developed include hydrocarbons such as acenes (see an example of patent related art below), sulfur-containing compounds such as thiophenes, and nitrogen-containing compounds such as phthalocyanines. The high molecules developed include poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) and poly(3-hexylthiophene) (P3HT).
PCT Application No. WO 03/016599 is the above-mentioned example of patent related art.
Tetrahedron Lett., Vol. 45, 7943-7946 (2004) is an example of non-patent related art.
In general, the low-molecular materials offer higher mobility than the high-molecular materials, but lack a high solvent solubility, thereby resulting in poor productivity. Improving their solvent solubility allows employment of an inkjet method or the like, which can lead to cost reduction. Accordingly, there has been a demand for a novel low-molecular organic semiconductor material that can offer improved carrier mobility and solvent solubility.